1. Field of the Invention
This invention relates generally to a graphics display capability in a data processing system, and more particularly to a hardware apparatus and method for permitting the selective blanking of the graphics portion of the display on a scan line basis without affecting the graphics display memory.
2. Description of the Prior Art
The graphics option of a computer system permits the system to display point-addressable graphics. This option is aimed at the business graphics marketplace where the ability to easily generate and modify pie charts, line charts and so forth are the prime objective. In many of these systems graphics and alphanumeric text are displayed visually. This allows the relationship between many variables of the business to be presented in pie chart or bar graph form. Graphics can be further utilized to display and manipulate mechanical or other electronic type designs.
In a system where text and graphics must share the same viewing screen area, it is difficult to read the text when both are present. What is needed is a system which allows blanking of a portion of the graphics portion that is displayed in order to highlight the display of the alphanumeric character. The prior art solved this problem by concentrating on the control of the display address to provide such window capabilities. This required excessive hardware to control the counters and multiplexing, and subsequently the addressing of each pixel. Accordingly, additional costs in the form of hardware was added to the computer system, and more importantly, it increased the processing time thereby reducing the overall system throughput.